The process for brewing beer based on grain, normally includes the steps of malting, milling, mashing, lautering, boiling, fermenting, conditioning and filtering.
Mashing
Mashing is the process of combining a mix of milled grain (typically malted barley with supplementary grains such as corn, sorghum, rye or wheat), known as the “grain bill”, and water, known as “liquor”, and heating this mixture in a vessel called a “mash tun”. Mashing allows the enzymes in the malt to metabolise the starch in the grain into sugars, typically maltose to create a malty liquid called wort. Conventionally there are two main methods—infusion mashing, in which the grains are heated in one vessel; and decoction mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature. The mashing process which can involve pauses at certain temperatures, is normally performed in a “mash tun” which is an insulated brewing vessel. The end product of the mashing process is called a “mash”.
Historically a mash rake was used in the mashing process. The mash rake was an instrument made of wood with a long handle, somewhat resembling an oar with large holes in the blade. The mash rake churns the mash to ensure that it is appropriately mixed and that the liquid can access the solid material in order to extract sugar from the solid material. Modern brewers, use mechanical power-rakes to mix the mash instead of traditional manual mash rakes.
Mashing usually takes 1 to 2 hours, and during this time the various temperature pauses activate different enzymes depending on malt type, level of modification and the brewer's intentions. The enzyme activity converts starches of the grains to dextrins and then to fermentable sugars such as maltose. A mash pause or rest between 49-55° C. activates various proteases, which digest proteins to avoid protein clouding of the beer. This rest is generally used only with undermodified (undermalted) malts which are decreasingly popular in Germany and the Czech Republic, or non-malted grains such as corn and rice, which are widely used in North American beers. A mash rest at 60° C. activates β-glucanase, which digests gummy β-glucans in the mash, thus causing the sugars to flow more freely later in the process. Finally, a mash rest temperature of 65-71° C. is used to convert malt starches to sugar, which is then usable by the yeast during the fermentation part of the brewing process. Duration of the rests and varying pH also affect the sugar composition of the resulting wort.
Lautering
Lautering is the separation of the clear liquid wort (containing the sugars extracted during mashing) and the residual grain.
The lautering process usually consists of the three steps of mashout, recirculation and sparging.
Mashout is the term for raising the temperature of the mash to about 77° C. which stops the enzymatic conversion of starches to fermentable sugars, and makes the mash and wort more fluid. The mashout step can be done by using external heat, or simply by adding hot water.
The recirculation step consists of drawing off wort from the bottom of the mash, and adding it to the top. Lauter tuns typically have slotted bottoms to assist in the filtration process. The mash itself functions much as a sand filter to capture mash debris and proteins. This step can be monitored by the use of a turbidometer to measure solids in the wort liquid by their opacity.
The sparging step is the trickling of water through the grain to extract sugars. This step is very sensitive to temperature and pH conditions as these parameters may result in extraction of tannins from the grain husks resulting in a bitter brew. Sparging is typically conducted in a lauter tun.
In many commercial breweries sparging is performed by a continuous process sparging meaning that when the wort reaches a desired level above the bed of settled grain, water is added at the same slow rate that wort is being drained. The wort thus gradually becomes weaker and weaker, and at a certain point, addition of water is discontinued.
The lautering process is normally performed either in a mash tun fitted with a false bottom, a mash filter or most frequently in a lauter tun.
A lauter tun is the traditional vessel used for separation of the extracted wort. While the basic principle of its operation has remained the same since its first use, technological advances have led to better designed lauter tuns capable of quicker and more complete extraction of the sugars from the grain.
A false bottom in a lauter tun has thin slits to hold back the solids and allow liquids to pass through. The settled solids rather than the false bottom form a filtration medium and retains small solid particles, allowing the otherwise cloudy mash to run out of the lauter tun as a clear liquid.
Run off tubes are evenly distributed across the bottom, with one tube servicing about 1 m2 of area. Typically these tubes have a wide, shallow cone around them to prevent compaction of the grain directly above the outlet. Traditionally the run-off tubes flowed through swan-neck valves into a wort collection grant. This system led to excessive oxygen uptake and thus such systems have gradually been replaced either by a central wort-collection vessel or the arrangement of outlet ports into concentric zones, with each zone having a ring-shaped collection pipe. Public brewhouses however often maintain the swan-neck valves and grant for their visual effect.
Quality lauter tuns have rotating rake arms with a central drive unit. Depending on the size of the lauter tun, there can be between two and six rake arms. Cutting blades hang from these arms. The blade is usually wavy and has a plough-like foot. Each blade has its own path around the tun and the whole rake assembly can be raised and lowered. Attached to each of these arms is a flap which can be raised and lowered for pushing the spent grains out of the tun. The brewer, or better yet an automated system, can raise and lower the rake arms depending on the turbidity (cloudiness) of the run-off, and the tightness of the grain bed, as measured by the pressure difference between the top and bottom of the grain bed.
There must be a system for introducing sparge water into the lauter tun. Most systems have a ring of spray heads that insure an even and gentle introduction of the sparge water. The watering system should not beat down on the grain bed and form a channel.
Large breweries often have self-closing inlets on the bottom of the tun through which the mash is transferred to the lauter tun, and one outlet, also on the bottom of the tun, into which the spent grains fall after lautering is complete.
Some small breweries use a combination mash/lauter tun, in which the rake system cannot be implemented because the mixing mechanism for mashing is of higher importance. The stirring blades can be used as a rake, however typically they cannot be moved up and down, and additionally they would disturb the bed too much were they used deep in the grain bed.
A lauter tun is disclosed in U.S. Pat. No. 3,782,551 wherein wort is produced by filtering mash in a vessel with a filtering sleeve fixed to the vessel. The wort produced by the vessel can be removed in separated streams, and, in addition, an agitator is used for mixing the water and the mash.
Another solution discussing separation of wort from mash is described in U.S. Pat. No. 4,844,932, where the mashing is carried out by use of a cross-flow separation filter, which filter may consist of a diameter shell within which a tubular filter is housed. The wort is produced in a four-step separation process wherein a reverse flow is mentioned in connection with the mash becoming resident on the filter or clogging the pores of the filter.
WO 98/20956 (Performance Pool Products Ltd) discloses a filter insert for a water filtration device. The insert is fixedly mounted inside a larger container. Water can be pumped into the filter insert, and be drawn from outside of the filter insert. The flow can be reversed (see FIGS. 5a and 5b). The insert cannot be moved inside the outer container and cannot be removed without opening the container.
U.S. Pat. No. 3,782,551 (Soldan) discloses a lauter tub with a filter insert. The filter is fixed inside the lauter tub and defines an internal volume which is almost as large as the internal volume of the lauter tub.
U.S. Pat. No. 4,793,243 (Lenz and Lenz) discloses a lauter tun with filter inserts that can be lowered into the lauter tun. The mash is present outside the filter inserts. Furthermore, the filter inserts have an open bottom. During lautering, liquid is drawn into the filter inserts and through a mesh in the bottom of the lauter tun. The filter inserts serve to increase the filter area.
DE 10 2008 039 374 (Krones AG) discloses a lauter tun with inserted tubes with mesh or filter walls. The inserted tubes serve to draw filtered liquid from the lauter tun. Pressure is applied to the lauter tun in order to increase the rate of extraction. The mash is placed outside the filter inserts. It appears that the liquid can be circulated through the lauter tun.
GB 1,149,476 discloses a clarifying tun for filtering brewer's mash comprising a container having inclined walls, wherein the container can be lowered into the lauter tun such that the inclined walls of the container are dispersed into the mash of the lauter tun. The wort is eluted through a discharge pipe at the top side of the lauter tun.